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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


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Old 12-18-2009
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Yanmar not making RPM

Ok this one has me stumped. I have a Yanmar 3GMF and can only make 2000 RPM's. My guess is that I'm leaving a lot of power untapped by not getting close to the max of 3200. Also when I recently opened up the throttle all the way, the power was reduced and a lot of back smoke and what appeared to be carbon came out the exhaust. I checked the intake and saw that it was full of black soot. It look exactly like what was coming out the exhaust.

Could this be culprit for not getting to 3200 RPM? Should I take off the intake and clean it or is it normal to have soot buildup in it? Could a fouled prop be the cause of lack of RPM (bottom and prop was done 9 months ago). Could the pitch of the prop be wrong? Since this is a fairly new boat to me, I don't have any history on what is normal.

A few more points. I can get max RPM when in neutral. The engine has about 350 hrs on a rebuild. I just recently (4 months ago) added a fuel treatment that allow kills algae build up and keeps the fuel fresh.

Thank for the help....bf

Last edited by Flyyboy; 12-18-2009 at 05:16 PM. Reason: Added additional information
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Old 12-18-2009
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What is the hull speed of your boat and how fast are you travelling at 2000RPM and can you reach your hull speed under ideal conditions under sail? (If not, your hull might be excessively fouled).
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Old 12-18-2009
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Your prop could be fouled or you could have the wrong prop. Have you seen higher rpm while in gear before?
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Quote:
Originally Posted by Zanshin View Post
What is the hull speed of your boat and how fast are you travelling at 2000RPM and can you reach your hull speed under ideal conditions under sail? (If not, your hull might be excessively fouled).
I can go much faster under sail. My hull speed is about 6 Kts. I can only get about 3 kts or so at 2000 RPM. I do remember going faster at one time on engine alone but I don't know what the RPM was.
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Quote:
Originally Posted by Gene T View Post
Your prop could be fouled or you could have the wrong prop. Have you seen higher rpm while in gear before?
My tach was broken for a long time so I can't tell if I have ever achieved a higher RPM. However, I do remember going aground on a sandy bottom as was able to power off. I'm not sure that I could do this now. Seems the power has diminished. I wonder if the fuel additive could have caused any growth in the diesel tank to end up in the filters. I just had a Racor installed at the last haul-out in April 09.

I'm in a new marina since Hurricane Ike destroyed my previous slip/marine. There seems to be a lot of growth at the water line than I've seen before. This new marine seems to foster marine growth. Could a prop that was spotless in April have enough growth on it that it could cause this type of scenario?
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Old 12-18-2009
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Quote:
Originally Posted by Flyyboy View Post
Ok this one has me stumped. a lot of back smoke and what appeared to be carbon came out the exhaust. I checked the intake and saw that it was full of black soot. It look exactly like what was coming out the exhaust.
What do you mean by "the intake" mentioned above???
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Old 12-18-2009
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Sounds like low compression. Rings or valves. Get a mechanic to do a compression test.
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Old 12-18-2009
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I would check your exhaust pipe coming out of engine. If it is hot you have a problem. Just recently I replaced mine.
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Fouled prop, fouled bottom, fouled air cleaner, corroded mixing elbow......
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Quote:
Originally Posted by Faster View Post
What do you mean by "the intake" mentioned above???
I meant to say the intake manifold. I took off the air filter and could see a lot of soot just behind the opening. I used a white rag to wipe as much as I could reach with my fingers. It is full. Someone told me this happens when a diesel idles to much. It would by my guess that the intake manifold should be clean and not full of soot. But thats just a guess.

Thank everyone for their response...
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